Shifting Towards Offshore Wind Energy—Recent Activity and Future Development

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Energy Policy 53 (2013) 136–148

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Energy Policy

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Shifting towards offshore wind energy—Recent activity and future development

J.K. Kaldellis n, M. Kapsali

Lab of Soft Energy Applications & Environmental Protection, TEI of Piraeus, P.O. Box 41046, Athens 12201, Greece

HIGHLIGHTS c An overview of the activity noted in the ﬁeld of offshore wind energy is carried out. c Emphasis is given on the current status and future trends of the technology. c Wind energy production and availability issues are discussed. c Economic issues such as investment and energy production costs are also analysed. article info abstract

Article history: To date, most of the existing wind farms have been built on-land but during the last few years many Received 10 February 2012 countries have also invested in offshore applications. The shift towards offshore wind project Accepted 11 October 2012 developments has mainly been driven by European energy policies, especially in north-west countries. Available online 21 November 2012 In offshore sites the winds are stronger and steadier than on-land, making wind farms more productive Keywords: with higher capacity factors. On the other hand, although offshore wind energy is not in its infancy Availability period, most of the costs associated with its development are still much higher from onshore Reliability counterparts; however some recent technological progress may have the potential to narrow this Levelized cost gap in the years to come. In the present work, an overview of the activity noted in the ﬁeld of offshore wind energy is carried out, with emphasis being given on the current status and future trends of the technology employed, examining at the same time energy production and availability issues as well as economic considerations. & 2012 Elsevier Ltd. All rights reserved.

1. Introduction Up to now, wind energy development has mainly taken place onshore. Offshore wind power technology comprises a relatively During the last 20 years, many countries all over the world new challenge for the international wind industry with a demon- have invested in the wind power sector in view of facing the stration history of around twenty years and about a ten-year rapidly increasing population and the limited fossil fuel resources commercial history for large, utility-scale projects. In the end of along with the adverse impacts of conventional power generation 2011, worldwide wind power capacity reached 240 GW (WWEA, on climate and human health. Wind energy is currently consid- 2012), from which, 2% comprised offshore installations. The main ered as an indigenous, competitive and sustainable way to motivation for moving offshore, despite the low or even null achieve future carbon reductions and renewable energy targets impact on humans and the opportunity of building wind farms in but issues such as the scarcity of appropriate on-land installation coastal areas close to many population centres, stemmed from the sites or public concerns related to noise, visual impact, impact on considerably higher and steadier wind speeds met in the open birdlife and land use conﬂicts often block its future development sea, even exceeding 8 m/s at heights of 50 m. Compared to the (Esteban et al., 2011; Kaldellis et al., 2012). As a result, a onshore counterpart, offshore wind energy has greater resource substantial shift towards the vast offshore wind resources has potential, which generally increases with distance from the shore. been made and an incipient market has emerged, i.e. offshore This fact results to considerably higher energy yield (Pryor and wind power. Barthelmie, 2001), as the power output is theoretically a function of the cube of the wind speed. However, the net gains due to the higher speciﬁc offshore energy production are counterbalanced

n by the higher capital, installation and maintenance costs and so Corresponding author. Tel.: þ30 210 5381237; fax: þ30 210 5381467. E-mail address: [email protected] (J.K. Kaldellis). the economic prospects of offshore wind energy utilisation are URL: http://www.sealab.gr (J.K. Kaldellis). not necessarily better than the onshore ones.

As far as the technology employed is concerned, it should be In the following years, relatively small offshore wind power noted that the design of offshore wind power projects has been projects were installed in the United Kingdom, Denmark, the based considerably on the long-term experience gained from Netherlands and Sweden, at distances of up to 7 km from the on-shore wind farms and from the oil and gas industry, while coast and depths of up to 8 m. Multi-megawatt wind turbines the commercial wind turbines used, currently having capacity appeared later, along with the opportunity of experiencing deeper ratings up to 5 MW, comprise adaptations from land-based counter- waters in the sea. In 2000, the construction of the first large-scale parts. However, offshore wind turbine technology is evolving at a offshore wind farm of ‘‘Middelgrunden’’ with a total rated power fast pace and thus much larger machines are expected in the of 40 MW (20 wind turbines of 2 MW each) ended 2 km outside of foreseeable future, specifically constructed for offshore use, which the harbour of Copenhagen in Denmark, where the seabed is will likely benefit from economies of scale resulting in significant situated between 2.5 and 5 m under sea level. The demonstration cost reduction. project of ‘‘Middelgrunden’’ in Denmark led the way for two All the above issues are analysed in this work. More precisely, larger offshore wind power projects, i.e. Horns Rev I (160 MW) in the objective of the present study is to provide a short review of 2002 and Nysted (165.2 MW) in 2003. However, the construction the activity noted in the field of the offshore wind energy at a costs of these projects were higher than anticipated, while some global level, emphasising on global market issues, current status unexpected failures occurred, resulting mainly from the turbines’ and future trends of the technology employed, examining at the exposure to harsh wind and wave conditions. It was such draw- same time energy production and availability issues as well as backs that held back development of the offshore wind power economic considerations such as investment and associated costs market for a respectable time period (Fig. 1). Nevertheless, great of electricity generation. efforts made by manufacturers and developers in order to identify and improve problems associated with this stage (Musial et al., 2010) eventually led the way for a number of new commercial offshore wind farm installations, all located in European waters. 2. Global offshore wind energy activity The year 2010 was a record-breaking year for the European offshore wind energy market. New installations accounted for According to the existing literature, the first documented about 900 MW (Fig. 1) (which was about 10% of all new wind theoretical concepts for installing wind turbines at sea were power installations) (EWEA, 2011). As for the end of 2011, 235 developed in Germany in the early 1930s by Hermann Honnef. new offshore wind turbines, with a total capacity of about Almost forty years later, off the coast of Massachusetts, Professor 870 MW, were fully connected to the power grids of the UK, William E. Heronemus introduced the idea of large floating wind Germany, Denmark and Portugal. In total, as for the end of 2011, turbine platforms (Heronemus, 1972). None of these early visions there were almost 1400 offshore wind turbines fully grid con- became reality however. The first offshore wind power test nected with a total capacity of about 3.8 GW (Fig. 1) comprising facility was eventually set up in Sweden, twenty years later, in 53 wind farms spread over ten European countries. 1990. It was a single wind turbine of 220 kW rated power, located As of February 2012, the Walney wind farm in the United at a distance of 250 m from the coast, supported on a tripod Kingdom is the largest offshore wind farm in the world structure anchored to the seabed about 7 m deep. (367 MW), followed by the Thanet offshore wind project The first full-scale development of offshore wind power projects (300 MW), in the UK. The London Array (630 MW) is the largest was driven largely by commercial aspirations of the European wind project currently under construction which is also located in the industry, considering oceans as a feasible solution to compensate UK. In total, 18 new wind farms, totalling 5.3 GW are currently for the scarcity of onshore sites. The first commercial offshore wind under construction and 18 GW are fully-consented in twelve farm was commissioned in 1991 in Denmark, in shallow water European countries with Germany possessing almost 50% of the (2–6 m deep), 1.5–3 km north from the coast of the island of total consented installations (EWEA, 2012). Once completed, Lolland, near the village of ‘‘Vindeby’’. This small wind farm, which Europe’s offshore wind power capacity will reach 27 GW. is still in operation, consists of eleven stall controlled wind turbines Up till now vast deployment has taken place in Northern of total rated power 4.95 MW (450 kW each) all being placed on Europe, a situation expected to continue for the next few years as gravity-based foundations. The cost of construction for this project well. Actually, more than 90% of the global offshore wind farms is stated to be approximately 10 million Euros (SEAS-NVE, 2011). are located in European waters. The leading markets are currently

1000 4000

900 new capacity cumulative 3600

800 3200

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600 2400

500 2000

400 1600

300 1200

Annual Capacity (MW) Capacity Annual 200 800

100 400 (MW) Capacity Cumulative

0 0 1991 1992 1994 1997 1998 2005 2007 1995 1996 1999 2000 2004 2008 2009 2011 2001 2002 2003 2010 1993 2006

Fig. 1. Offshore wind farm installations in Europe. 138 J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148

2500

2093,7 2000

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1000 857,3 Power (MW)

500 246,8 233 200,3 195 163,7 26,3 25,2 25 2,3 2 0 UK China Japan Ireland Finland Norway Belgium Sweden Portugal Denmark Germany Netherlands

Fig. 2. Global installed offshore wind power by country (end of 2011). the UK, Denmark and the Netherlands with cumulative capacity Others: 6% ratings of 2094 MW, 857 MW and 247 MW respectively (as for Repower: 5% the end of 2011), see Fig. 2. By 2020, offshore wind power scenarios entail a quite ambitious development path with 75 GW installations worldwide, with significant contribution expected from the United States and China (EWEA, 2007). Siemens: 53% China, the world’s largest onshore wind power developer, with Vestas: 36% a total of about 62 GW by the end of 2011, erected the first large- Fig. 3. Wind turbine manufacturers’ cumulative share up to 2011 in Europe. scale commercial offshore wind farm (Donghai Bridge) outside Europe in 2009, adding 63 MW by year-end for a project that reached 102 MW upon completion in the early 2010. Thus, although offshore wind power development in China has much large-scale operational offshore wind power project at that time, delayed, the year 2010 marked the start of transition for the local with an average distance from the shore of about 53 km) named offshore wind power sector from research and pilot projects to ‘‘Alpha Ventus’’ in Germany in 2009. Sinovel also entered the operational wind farms. Today, China has about 230 MW (including market in 2009 with the SL3000/90, the first offshore wind an intertidal project) of offshore wind power installations. According turbine manufactured in China and installed in the ‘‘Donghai to the Chinese Renewable Energy Industries Association (CREIA) Bridge’’ project. More recently, General Electric re-entered the (CREIA, 2011), China is planning to exploit its vast offshore wind offshore wind market with the announcement of its 4.1 MW resources (Da et al., 2011) by greatly expanding its offshore capacity direct drive wind turbine, which is still under development to 5 GW by 2015 and 30 GW by 2020, as a result of the country’s (GE Energy, 2011). commitment for 40–45% (from the base year 2005) (Zhang et al., 2010) carbon emission reduction until 2020. On the other hand, as for the end of 2011, there are no offshore 3. Technology challenges wind power projects operating off the United States, which is the second world leader in land-based wind energy. The only 3.1. Evolution of offshore wind farms’ main characteristics approved project, after a decade-long process, is to be located off the coast of Massachusetts and is expected to comprise 130 Offshore, the size and capacity of wind turbines, as well as the 3.6 MW wind turbines that will be operational in 2012. However, total rated power of wind farms follow the onshore increasing U.S. offshore wind energy plans call for the deployment of 10 GW trend and even more since there are fewer political limits. While of offshore wind generating capacity by 2020 and 54 GW by 2030 at land-based sites the size of wind turbines, in terms of height (U.S. Department of Energy, 2011). and rotor diameter, is often restricted due to visual impacts, these Offshore wind power market is currently dominated by few limits are not usually encountered in marine environments. Thus, companies. On the demand side about ten companies or consortia as it may be observed from Fig. 4, wind turbine capacity has been account for all the offshore capacity presently in operation. Dong increasing steadily every year since 1991. In the 90s, offshore Energy (Denmark), Vattenfall (Sweden) and E.on (Germany) are wind turbine rated power was well below 1 MW, while 2003 was the leading operators, all being giant European utilities. On the the first year of introducing commercial wind turbines above supply side, Siemens (formerly Bonus Energy A/S) and Vestas are 2 MW. In 2005, one offshore wind farm went online using 3 MW by far the leading wind turbine manufacturers worldwide in turbines, setting a new benchmark for the industry (EWEA, 2010). terms of installed capacity. In Europe, their cumulative share Since then, offshore wind turbines installed generally in the range reaches 90% (Fig. 3). However, there are several other manufac- between 2 and 5 MW although prototypes of power up to 7 MW turers that are now developing new offshore wind turbines’ types and even higher are currently tested, indicating the manufactur- which are close to commercial viability. For instance, both ing trends concerning future wind turbines operating in maritime Repower Systems and AREVA Multibrid installed commercial environments. On top of that, wind farms’ total capacity has turbines of 5 MW under a pilot project (comprising the deepest increased as well. Before 2000, average wind farm size was below J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148 139

6 Bubble area represents power capacity of the wind farm

2 Turbine capacity(MW) Turbine

0 1990 1995 2000 2005 2010

Fig. 4. Size evolution of existing offshore wind farms and wind turbines (2010).

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0 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 1995 1996 1997 1998 1991 1992 1993 1994 1999

Fig. 5. Evolution of average distance from shore and water depth.

20 MW. Today, the experience has grown significantly so that gravity-based one (Fig. 6), both comprising fixed bottom struc- many countries are building large (average size of projects tures mainly employed in shallow water depths. Fig. 7 sum- exceeds 150 MW), utility-scale offshore wind farms or at least marises the main support structures for offshore wind turbines in have plans to do so. terms of maturity and water depth. Nevertheless, the vast majority of the existing large-scale At this point it should be mentioned that during the last years commercial projects still use shallow-water technology (located the floating concept (i.e. mounting a wind turbine’s tower on a at less than 30 m water depth) although the idea of going deeper floating platform) has been introduced in order to eliminate as is gradually moving closer towards implementation. Actually, the much as possible the visual impact and take advantage of the average water depth remains below 20 m (Fig. 5), excluding the higher and steadier wind speeds found in deep waters. At deeper first full scale floating wind turbine (Hywind) which was installed water sites, the fixed bottom support structures are inapplicable in 2009 off the Norwegian coast at a water depth of 220 m. On the because as depth increases loading increases too and this requires other hand, the average distance from shore ten years ago was larger structural dimensions which are economically non-viable. below 5 km, while today is close to 30 km—confirming that Nevertheless, floating wind turbine technology is still immature offshore wind turbines are installed increasingly away from the (Fig. 7) and is associated with increased technical risk which shores (Fig. 5). tends to drive costs upwards. So far, there is no standard type of support structure suitable Up till now (end of 2011), four floating wind turbine concepts for all kinds of seabed conditions and depths. As mentioned have been installed (see for example Fig. 8), i.e.: above, the majority of offshore wind power projects is currently located in shallow water and employs fixed bottom structures An 80 kW floating wind turbine was deployed 113 km off the suitable for small (shallow) to moderate (transitional) depths. coast of Italy in 2007. It was then decommissioned at the end More specifically, various support structures have been used up of 2008 after completing a planned test year of gathering till now, with the most common types being the monopile and the operational data. 140 J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148

Gravity-based: Jacket: 2% Gravity-based: 21% 35% Others: 2% 2000 2011

Monopiles: 65% Monopiles: 75%

Fig. 6. Share of support structures’ types for the in operation wind farms. Based on data found in (EWEA, 2010, 2012)).

Monopiles

Gravity-based

Jackets

Tripiles

Tripods Developed Mature Maturity Floating concepts Developing Suction buckets

Shallow water30m Transitional water 60m Deep water

Fig. 7. Main support structure technology in relation to water depth.

Fig. 8. Floating wind turbine prototype concepts which have already been installed (Left: SeaTwirl, Middle: Hywind, Right: WindFloat) (Seatwirl, 2012; Renewable energy focus, 2012; Gotpowered, 2012).

The first large-capacity, 2.3 MW floating wind turbine wind turbine off the coast of Sweden in 2011. It was tested and ‘‘Hywind’’, became operational in the North Sea off the coast recently de-commissioned. of Norway in 2009 in 220 m water depth and is still operational (as of 2011). It is worth mentioning that this wind turbine, in 2011, produced about 10.1 GWh which results in a It should be noted that, the world’s first full scale floating wind capacity factor of more than 50% (Statoil, 2012). turbine ‘‘Hywind’’ cost was around 400 million kroner (or around In October 2011, a WindFloat Prototype was installed 4 km 54 million Euros) including construction and further development offshore a coast of Portugal in approximately 45 m depth. The (R&D) related to the specific wind turbine concept. Although this WindFloat was fitted with a Vestas V80 2 MW offshore wind cost may seem unreasonably high it must be underlined that the turbine. specific project was the first of its kind and that its demonstrative Finally, SeaTwirl deployed a vertical axis (with blades above nature required considerable R&D efforts as well as monitoring of the water and the generator below) floating grid connected its operating behaviour. J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148 141

3.2. Energy production and availability issues existence of many low density population areas which benefit of high wind speeds and enable the siting of wind farms. As offshore wind turbines operate far from shores in harsh On the other hand, one of the main advantages of offshore environments, the need for high reliability and low operation and wind power is that the wind turbines may have the ability to maintenance (O&M) costs is higher than for on-land applications. demonstrate quite higher capacity factors than onshore counter- In fact, O&M costs may be up to three times higher than those of parts (as a result of the higher mean power coefficient which is land-based systems (Rademakers et al., 2003; Musial et al., 2010), usually met in offshore installations), typically ranging from 20% exceeding 20% of the overall cost of these projects during lifetime to 40%. In this context, Fig. 9 depicts the annual capacity factor of (Blanco, 2009). One of the main causes for these high costs is the several representative offshore wind farms across Europe as rather frequent need for employing expensive transportation recorded for the year 2011. One may see that capacity factor means in order for the personnel to reach the wind farm and values, in some cases, even reached 50%, however, this is not the perform the service work required (Bussel and van Zaaijer, 2001). rule since there are cases where the recorded capacity factor may In this context, high operational reliability and adequate main- be quite low mainly as a result of the combination of extended tenance capability (mainly determined from accessibility restric- downtimes due to several system failures and the tough conditions) are two interrelated and critical issues for safeguarding the tions usually met in marine environments. long-term operation of an offshore wind farm, in both technical As a result of the above, the critical role of the technical and economic terms. For that reason, parameters such as mini- availability over a period of time for the energy production of a misation of maintenance requirements as well as maximisation of given wind turbine or an entire wind farm is reflected. At this access capability are of great importance during the design point, one should also note that technical availability of a wind procedure of a project. turbine depends, among others, on: It is well known that the energy yield of a wind farm during a specific time period (e.g. 8760 h) is estimated as a function of the The technological status (experience gain effect throughout installation’s capacity factor ‘‘CF’’ (or utilisation factor of the local the years) of the installation at the time it went online wind potential) and the rated power of the wind turbines. The (increasing experience in both production and operation issues technical availability, which is actually configured by the hours of in the offshore sector suggests that the failure rate decreases operation of a given wind turbine or wind farm by considering the and the reliability increases respectively). time period that the machine is kept out of operation due to e.g. The technical availability changes (aging effect) during the scheduled maintenance, unforeseeable events (e.g. lightning, installation’s operational life. sudden fault of a machine) etc. (Herbert et al., 2010), may be a The accessibility difficulties (accessibility effect) of the wind determining factor to the CF of an installation. Obviously, many farm under investigation. This parameter is, as aforemen- days of downtime during a specific time period will reduce the tioned, of special interest for offshore wind parks, especially availability of the wind farm and therefore its energy production during winter, due to bad weather conditions (high winds and and CF over that time period. However, the amount of energy loss huge waves suspend the ship departure, thus preventing will depend on when the downtime occurs, e.g. the impact of the maintenance and repair of the existing wind turbines). availability on the energy performance of the plant will be much higher when the local wind potential is high. Nowadays, contemporary land-based wind turbines and wind In general, actual capacity factors for onshore wind farms farms reach availability levels of 98% or even more (Kaldellis, 2002, oscillate across time and regions, with an average value being 2004; Harman et al., 2008) but, once these wind turbines are placed between 20 and 30%. For instance, the average European value offshoretheaccessibilitymaybesignificantly restricted, thus causing between 2003 and 2007 has been recorded at about 21%. The a considerable impact to the availability of the wind farm and in turn highest values have been recorded for Greece and the UK (i.e. to the energy and economic performance of the whole project. This is equal to 29.3% and 26%, respectively) (Boccard, 2009) due to the not always the case however; apart from the distance from the shore,

55 2009 2009 50 2002 2010 45 2003 2009 2008 40 2006 2004 2007 35

30 2000 25 CF (%) 1991 20 2001 15

0 Nysted (UK) (UK) Vindeby (Denmark) (Denmark) (Denmark) Rodsand 2 (Denmark) (Denmark) Barrow (UK) Horns Rev 2 Horns Rev 1 (Sweden) (Denmark) Beatrice (UK) Burbo Bank 1 Scroby Sands Middelgrunden Yttre Stengrund Robin Rigg (UK) Hywind (Norway)

Fig. 9. Capacity factors for several offshore wind turbine projects for the year 2011 along with projects’ year of commissioning. 142 J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148 the accessibility to a wind farm’s installation site depends also on 4. Economic considerations several other parameters such as local climate conditions and the type and availability of the maintenance strategy adopted (the 4.1. Capital cost of investment limited size of some wind farms does not always justify the purchase of a purpose built vessel so there may be significant delays if the As stated earlier, in offshore sites the winds are stronger and vessel is, for example, away for another assignment). Thus, there are steadier than on-land, making wind farms more productive with cases where the impact may be more or less significant than the higher capacity factors. On the other hand however, as offshore expected one. wind energy is a newcomer, most of costs associated with its A case with low recorded availability is North Hoyle offshore development are still much higher compared to onshore counter- wind farm, which is located in the UK, at an average distance from parts (Green and Vasilakos, 2011), although some recent techno- the shore equal to 8 km (see also Table 1 where recorded logical progress in terms of more efficient production patterns availability data for several wind farms are presented). As it is may have the potential to narrow this gap in the near future. mentioned in (BERR, 2005), the availability of this wind farm In general, for most of the existing projects, current turnkey (or during a one-year period (2004–2005) was recorded equal to 84%. capital) offshore wind power costs are estimated to be within the The most notable sources of unplanned maintenance and down- wide range of 1300–2500 h/kW while for onshore installations time have occurred due to termination of cable burial and rock they are significantly lower, i.e. approximately 1100–1500 h/kW dumping activities as well as high-voltage cable and generator (Ecofys, 2011) for newly-established projects in Europe, while in faults. It is worth mentioning that the downtime recorded splits some emerging markets these costs may be lower due to cheaper to 66% owed to turbine failure, 12% to construction activities, 5% labour works, grid connection and upgrade issues etc. (Blanco, to scheduled maintenance and 17% to site inaccessibility due to 2009). Capital costs of offshore wind power projects can be divided harsh weather conditions. Another example with even lower into the following main categories: availability (67%) is the case of Barrow offshore wind farm (see also Table 1), also located about 8 km far from shore, in the UK. Cost of wind turbines (e.g. blades, rotor, tower, condition The total average availability of this project is quoted as 67% for monitoring etc.). one-year period between July 2006 and June 2007. This low Cost of electrical infrastructure (underwater cables for collec- availability is due to a number of wind turbine faults, mainly tion of power and transmission to the grid, substations, generator bearings and rotor cable faults combined with low transformers etc.). access to the site because of high waves during that time period. Cost of support structures.

Table 1 Availability of several offshore wind farms. Based on data from BERR (2009).

Project Period Year Capacity of Average Recorded Comments online each turbine distance from availability (MW) shore (km) (%)

Barrow—UK July 2006 –June 2007 2006 3 8 67 The low availability is due to a number of wind turbine faults, mainly generator bearings and rotor cable faults combined with low access to the site because of high waves Kentish Flats—UK January 2006– 2005 3 9 87 Availability was relatively low mainly due to faults on December 2006 generator bearings and rotor cables for the slip ring unit and gearbox failures Kentish Flats—UK January 2007– 2005 3 9 73.5 Availability has been severely hampered during 2007 mainly December 2007 due to bearing failures in the planetary gear stage North Hoyle—UK July 2004 –June 2005 2003 2 8 84 Availability was mainly affected due to termination of cable burial and rock dumping activities, high-voltage cable fault and generator faults as well as site inaccessibility due to harsh weather conditions North Hoyle—UK July 2005 –June 2006 2003 2 8 91.2 Availability was mainly affected due to extended outages due to generator bearing faults and gearbox faults North Hoyle—UK July 2006 –June 2007 2003 2 8 87.4 Availability was mainly affected by gearbox bearing faults and chipped teeth, resulting in gearbox replacements. It should be noted that gearbox replacement was delayed by several months as no specialist vessels were available. Other major component failures include rotor cable faults, circuit breaker issues etc. Scroby Sands—UK January 2005– 2004 2 3 84.2 Availability was mainly affected due almost to problems with December 2005 bearings in the gearbox. Furthermore, there were a total of 143 adverse weather days when access to the wind farm was prevented Scroby Sands—UK January 2006– 2004 2 3 75.1 Availability was mainly affected due to gearbox bearings and December 2006 generator failures. It should also be noted that there were a total of 76 adverse weather days when access to the wind farm was prevented Scroby Sands—UK January 2007– 2004 2 3 83.8 Technical Availability only suffered during November due to a December 2007 high number of waiting on weather days which delayed returning turbines to service following the generator replacement work Tunø January 1996–June 1995 0.5 6 98.3 Only one major problem was experienced on Tunø during this Knob—Denmark 1998 time period: In one turbine, the hydraulic unit serving the pitch mechanism and the brake was replaced, leaving the turbine idle for almost 3 weeks. Weather conditions prevented a faster response to the problem J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148 143

monopiles Thanet distance from shore: 12km 2010 high rise pile cap Donghai Bridge distance from shore: 11km tripods and jackets 53km Alpha Ventus distance from shore: 2009 monopiles Horns Rev II distance from shore: 30km monopiles Princess Amalia distance from shore: 8km 2008 monopiles Egmond aan Zee distance from shore: 10km 2006 gravity-based Nysted distance from shore: 23km 2003

monopiles Horns Rev I distance from shore: 16km 2002 gravity-based 2000 Middelgrunden distance from shore: 3km

012345 million Euros/MW

Fig. 10. Indicative historical capital costs per MW of several offshore wind farms along with their year of commissioning.

70 offshore onshore

20 Share of the Capital Cost (%) 10

0 Turbine ex works, Support structure Electrical Design, Other including logistics infrastructure development and and installation permits

Fig. 11. Capital cost breakdown for offshore wind power projects in shallow water in comparison with onshore. Based on average data from (Blanco, 2009; EWEA, 2009b).

Cost of logistics and installation. and grid connection issues which are more expensive in case of Development and engineering costs (e.g. licensing procedures, offshore wind power projects, so the percentage of the turbine’s permits, environmental impact assessment studies etc.). contribution to total capital cost is less (EEA, 2009). Speciﬁcally, Other miscellaneous costs which are not included in the above the above discrepancies are related with the following key issues: categories. Foundations in offshore sites are much more expensive As one may easily obtain from Fig. 10, capital costs are not than on-land. For a conventional wind turbine installed standard, but they depend on a variety of factors such as distance on-land, the share of the foundation is approximately 5–9% from the shore, water depth, foundation technology employed (EWEA, 2009a) (see Fig. 11) while in an offshore site the etc., and thus can exceed by far the above 2.5 million h/MW respective cost may be up to 30% of the initial capital invested threshold for a distinct case. For example, for ‘‘Alpha Ventus’’ and even higher in case of very deep waters and unfavourable wind farm the capital cost per MW exceeded 4 million h mainly soil conditions. due to the demonstrative nature of the project. Construction and installation techniques adopted for offshore Fig. 11 presents data concerning main capital cost estimates projects are still immature and thus more expensive. In general, for offshore wind power projects located in shallow waters at larger distances, installation costs increase because of the (o30 m depth) in comparison with onshore. The estimates for greater travelling time needed for reaching the site. In addition, the offshore turbine’s contribution are about 45% to total capital weather conditions usually become worse, as distance from cost whereas the initial cost of a project on-land is dominated by shore increases, thus making installation of a project a quite the cost of the turbine itself, which is approximately 2 times difﬁcult task (Bilgili et al., 2011). higher (80%) (in absolute terms). These cost differences are Offshore, electrical connection issues generate substantial mainly attributed to the support structure, installation process additional costs compared with onshore installations. 144 J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148

Higher technical risks at offshore sites and siting complexity substantially higher than those of land-based systems (two or which drive costs up. three times greater) (Rademakers et al., 2003), exceeding 20% of the total levelized cost, while in some cases they can even reach As the distance of wind turbines from shore increases, instal- up to 30%, mainly due to difficult and expensive access to the site. lation and electrical infrastructure costs are driven upwards. The Concluding, it should be noted that due to the limited number construction of wind farms further from shore normally involves of offshore wind power projects currently being installed, accu- higher depths which may require more complex installation rate statistical trends of associated costs of development and procedures (e.g. special vessels capable of carrying larger wind operation, as is the case of onshore counterparts, are difficult to turbines and components) and more expensive equipment (e.g. be extracted yet. Water depth, distance from the shore, founda- support structures). Furthermore, greater distances, as aforemen- tions, grid connection issues, infrastructure required and O&M are tioned, result to an increase of the travelling time of the apparently determinant factors for the total energy cost during construction vessels in the sea. In addition to that, one should lifetime. Nevertheless, offshore wind energy is still under evolu- take into account a possible time-delay of the installation due to tion and requires special R&D efforts in terms of developing cost- harsher wind and wave conditions when moving deeper in the efficient O&M strategies, high reliability, site access solutions, sea. In this context, the additional time required for completing innovative components and improved and fully integrated ‘‘wind the installation due to ‘‘weather downtime’’ may reach 20–30% turbine-support structure’’ concepts. (EEA, 2009). Also, moving deeper implies a larger undersea cabling system for connecting the wind farm with the electrical grid and possibly the employment of an offshore substation, thus 5. Future expectations affecting significantly the electrical infrastructure costs. Based on official data, costs for offshore cables are between 500,000 and Offshore wind energy development has shown a quite 1 million Euros per km (International Association of Engineering unsteady progress since the beginning of its appearance but is Insurance, 2006). foreseen to expand significantly in the years to come and move from the pioneering phase to a large-scale global deployment. 4.2. Life-cycle cost Offshore wind power experienced a record growth in 2010. Total installed global offshore wind capacity, at the end of the In addition to the higher capital investment costs, offshore year, amounted to approximately 3 GW, out of which more than a projects have higher levelized costs of energy from onshore wind half was added in 2010 leading to an average growth rate which is farms. Broadly speaking, the cost of generating energy for a wind by far higher than the respective of the onshore wind energy power project is the sum of initial investment and O&M costs sector (WWEA, 2010). Currently (end of 2011), the total offshore (split into the fixed maintenance cost and the variable one) over capacity is nearly 4 GW. As for the future expectations, despite the operational life of the project (e.g. 25 years), divided by the the world economic and financial crisis which definitely may have total energy output of the project. Subsequently, the levelized an impact on the financing options available to investors, the cost of electricity generation is estimated as a unit of currency European Wind Energy Association has increased its 2020 target (life-cycle cost) per unit of energy produced (e.g. in b/kWh or to the challenging amount of 230 GW wind power capacity, hcent/kWh). including 40 GW offshore wind. As for 2030, the wind industry Current levelized costs of energy of land-based projects vary has also set the ambitious target of 400 GW of wind power within the range of 4.5–8.7 hcent/kWh while for offshore installa- installations in Europe, out of which 150 GW to be located tions respective costs are almost double, i.e. 6–11.1 hcent/kWh offshore and produce more than 550 TWhe of electricity (EWEA, (Blanco, 2009). It should be mentioned however, that offshore 2008; EWEA, 2009c). In fact, according to EWEA targets (EWEA, costs are determined by a quite high degree of uncertainty, 2009c), for the forecasted annual wind power installations up to mainly due to different policy measures and support mechanisms the year 2030 as well as for capacity prices equal to 1250 h/kW for adopted in several countries. onshore and 2400 h/kW for offshore (in 2005 constant prices), Estimated life-cycle cost (or total project cost during lifetime) investment in wind energy (both onshore and offshore) should breakdown for a typical offshore wind power project is presented reach h23.5 billion in 2020 and h25 billion in 2030 (Fig. 13). The in Fig. 12. As seen in the figure, costs are largely determined by a decade up to 2030 is projected to be almost stable, almost h25 range of parameters which extend far beyond the wind turbine billion annually, with a gradually increasing share of investments itself. Particularly, life-cycle cost is dominated by O&M costs however going offshore. while logistics, installation, support structures and electrical Nevertheless, apart from the aforementioned ambitious tar- infrastructure also obtain a considerable part (almost 1/3 of the gets and the undeniable progress met in the field of offshore wind total). It should be mentioned at this point that O&M costs are during the recent years, one should not disregard the fact that at

Other variable costs 11% Wind turbine 29% Over lifetime 32%

O&M costs 21%

Other capital costs Electrical infrastructure 1% Initial cost 11% 68% Project development and permits 4% Logistics and installation Support structure 10% 13%

Fig. 12. Life-cycle cost breakdown for a typical offshore wind farm. Based on data from (Musial et al., 2010; U.S. Department of Energy, 2011). J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148 145

Offshore 25 Onshore

15 billion Euro 10

0 2012 2016 2017 2019 2013 2015 2018 2020 2021 2022 2023 2024 2025 2026 2027 2029 2030 2010 2014 2028 2011

Fig. 13. Projected annual wind energy investments up to 2030. Based on scenarios included in (EWEA, 2009c). the moment, offshore wind farms represent only a very small Proposal with RES trading’’ scenarios (EC, 2008a, 2008b)), percentage of the global wind power capacity, in the order of 2%. although what is eventually estimated as economically feasible, Despite the fact that the ﬁrst project was built twenty years ago, when taking into account projected average levelized energy the offshore wind energy sector still remains under development costs, is eventually much less, i.e. 2600 TWhe, covering and thus exploration of prospects and technological trends is of however–in rough numbers–almost 2/3 of the projected electri- primary importance for determining its ability to compete with city demand. Accordingly, based on the corresponding results of onshore wind farms and more importantly with conventional the same report for 2030, the economically competitive wind electricity generation. resource potential could cover more than 80% of that time’s

In this context, evaluation of available offshore wind energy expected EU electricity demand (i.e. approx. 4400 TWhe (EC, potential and mapping of the most suitable regions is a big step 2008a, 2008b)). towards the promotion of the offshore concept. To this end, in Apart from the excellent potential of the wind energy resource August 2008, the project ‘‘NORSEWInD’’ officially started (under in many maritime locations, however, offshore wind energy is the EU’s 7th Framework Programme/duration: 2008–2012) aim- still faced with many unique technological challenges. Although ing at producing high quality Wind Atlases for the North, Irish and the technology has developed rapidly during the last years there Baltic Seas (NORSEWInD, 2012), see also Table 2. Furthermore, is a general view that further improvements can be expected in many interesting studies (e.g. de Castro et al., 2011; EEA, 2009; Lu terms of both energy performance and cost effectiveness, with et al., 2009; deVries et al., 2007; Capps and Zender, 2010; Zerta most R&D efforts currently concentrated in improving turbine et al., 2008) have been implemented so far to evaluate the long design and reliability and in developing the next generation of term technical potential of wind power, with most of them offshore ‘‘wind turbine-support structure’’ concepts. concluding that the amount of the wind resource poses no limit Today’s operational offshore wind turbines are adaptations due to its extreme abundance. However, significant differences from land-based proven technologies and, as mentioned above, among the estimated top limits in all these studies may be have rated capacity up to 5 MW. Nevertheless, design variations noticed, e.g. the technical potential of wind power which is currently being pursued include first, as mentioned in section 3, examined by de Castro et al. (2011) is found one or two orders an increase of turbine capacities to tens of MWs (de Vries, 2009) of magnitude lower than other technical potentials estimated in in order to maximise energy production and benefit from econo- similar studies. mies of scale and second, the adoption of advanced techniques in Relative to the evaluation of the European offshore wind view of increasing wind turbines’ reliability along with providing energy resources, the technically available as well as the con- faster, cheaper and more efficient maintenance. In this regard, strained1 and the economically competitive2 wind energy poten- experience gained through ongoing or completed projects such as tial are depicted in Fig. 14, for a time horizon up to 2030 (based the ‘‘UpWind’’ (funded under the EU’s 6th Framework Pro- on the results of the European Environmental Agency Report gramme/duration: 2006–2011) and ‘‘HiPRWind’’ (started in (EEA, 2009)). As one may see, the available offshore potential is 2010 as a part of the EU’s 7th Framework Programme) (Table 2) quite high, reaching 25,000 TWhe/year in 2020 (i.e. 7 times is considered highly valuable. The main scope of the former was greater than the projected electricity demand over that year the investigation of the limits of upscaling of very large wind

(approx. 4000TWhe) based on the ‘‘business as usual’’ and ‘‘EC turbines (up to approximately 20 MW/250 m rotor diameter) (Upwind, 2011), while the main aim of the latter is to unlock vast new deepwater areas for wind farms by doing research on 1 Environmental (Natura 2000 and other protected areas) and social con- very large, ﬂoating offshore wind turbines (HIPRWIND, 2011). straints are taken into account. For offshore installations, limitations such as As regarding expected capacity factors, it is stated that by shipping routes, military areas, oil and gas exploration and tourist zones are also 2020, at the European level, average values for offshore wind considered. could reach the quite high percentage of 40–45% (Boccard, 2009; 2 The wind resource potential that is considered as cost competitive in the light of projected average energy costs in the future based on European Commis- EWEA, 2008). These high values are attributed to a variety of sion’s baseline scenario (EWEA, 2008). concepts which have already been developed or are under 146 J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148

Table 2 Offshore projects under the EU 7th Framework Programme.

Project Acronym Funds by the Duration Scope FP7

Offshore Renewable Energy ORECCA 1.6 Mh 03/2010–8/2011 The objectives of this project are to create a framework for knowledge sharing Conversion Platforms— (18 months) and to develop a research roadmap for activities in the context of offshore Coordination action renewable energy (RE). In particular, the project will stimulate collaboration in research activities leading towards innovative, cost efficient and environmentally benign offshore RE conversion platforms for wind, wave and other ocean energy resources, for their combined use as well as for the complementary uses Marine Renewable Integrated MARINA 8.7 Mh 01/2010–06/2014 MARINA is a European project dedicated to bringing offshore renewable energy Application Platform PLATFORM (54 months) applications closer to the market by creating new infrastructures for both offshore wind and ocean energy converters. It addresses the need for creating a cost-efficient technology development basis to kick-start growth of the nascent European marine renewable energy (MRE) industry in the deep offshore Northern Seas Wind Index NORSEWIND 3.95Mh 08/2008 - 08/2012 NORSEWInD is a programme designed to provide a wind resource map Database (48 months) covering the Baltic, Irish and North Sea areas. The project will acquire highly accurate, cost effective, physical data using a combination of traditional Meteorological masts, ground based remote sensing instruments (LiDAR & SoDAR) and Satellite acquired SAR winds. The resultant wind map will be the first stop for all potential developers in the regions being examined, and as such represents an important step forward in quantifying the quality of the wind resource available offshore Reliability focused research on RELIAWIND 5.18 Mh 03/2008–03/2011 RELIAWIND consortium, for the first time in the European Wind Energy Sector, optimising Wind Energy (36 months) and based on successful experiences from other sectors (e.g. aeronautics) will systems design, operation jointly & scientifically study the impact of reliability, changing the paradigm of and maintenance: Tools, how Wind Turbines are designed, operated and maintained. This will lead to a proof of concepts, guidelines new generation of offshore (and onshore) Wind energy Systems that will hit & methodologies for a new the market in 2015 generation Future Deep Sea Wind Turbine DEEPWIND 2.99 Mh 10/2010–8/2014 The objectives of this project for new wind turbines are: (i) explore the Technologies (46 months) technologies needed for development of a new and simple floating offshore concept with a vertical axis rotor and a floating and rotating foundation, (ii) develop calculation and design tools for development and evaluation of very large wind turbines based on this concept and (iii) evaluate the overall concept with floating offshore horizontal axis wind turbines High Power, High Reliability HIPRWIND 11.0 Mh 11/2010–10/2015 The aim of the HiPRwind project is to develop and test new solutions for very Offshore Wind Technology (59 months) large offshore wind turbines at an industrial scale. The project addresses critical issues such as extreme reliability, remote maintenance and grid integration with particular emphasis on floating wind turbines

4,400 2030 Projected electricity demand

2020 4,000

2030 3,400 Economically competitive potential

2020 2,600

3,500 2030 Constrained potential

2020 2,800

2030 30,000 Technical potential 2020 25,000

0 5000 10000 15000 20000 25000 30000 35000 40000

TWhe

Fig. 14. Projected technical, constrained and economically competitive potential for offshore wind energy development in 2020 and 2030. development for increasing both wind turbines’ performance and Adoption of advanced techniques and materials through an reliability of offshore commercial wind power plants. Indicative integrated design of wind turbines to withstand the demanding examples in this field correspond to: sea conditions and incorporation of Condition Monitoring Systems (Amirat et al., 2009; OSMR, 2004), which can provide continuous The increase of wind turbines’ efficiency through the develop- inspection of the state of the plant (Braam et al., 2003; ment of new systems with reduced maintenance requirements Wiggelinkhuizen et al., 2007; Wiggelinkhuizen et al., 2008). (ReliaWind, 2012). Adoption of more efficient and newer drive-train concepts in Implementation of advanced maintenance strategies. view of increasing wind turbines’ reliability. J.K. Kaldellis, M. Kapsali / Energy Policy 53 (2013) 136–148 147

For the purpose of facilitating equipment transportation and significant. Among the main reasons which drive this growth are associated costs during installation process, the use of light- that the opportunities for wind development on-land become weight and cost-effective materials for the design of towers, increasingly limited, the existence of more consistent and higher drive-trains and support structures or even bringing back the winds in offshore sites, the absence of obstacles such as moun- idea of two-blade machines (Butterfield et al., 2005) (since visual tains, buildings and trees in marine environments, the low or impact is unlikely to be an important consideration offshore) even null impact on humans, the pressure to achieve renewable could comprise feasible options. Furthermore, in view of improving energy targets and finally the enabling of building offshore wind wind turbines’ reliability and providing cheaper installation farms in coastal areas close to many population centres. and maintenance, innovative ideas and strategies come to light. On the other hand, the most important drawback of offshore An example is the adoption of innovative logistic concepts (e.g. wind energy is the high costs associated with its development. enhancing port infrastructure) and improvement of the wind In fact, costs are still much higher from onshore counterparts but turbines’ ergonomy and accessibility either by means of increas- some recent technological progress in terms of more efficient ing the number of the purpose-built vessels or by incorporating production patterns (increase of the size of wind turbines, special landing stages for helicopters. At this point the increas- improvements in the design of the projects, increase of avail- ingly important role of the preventive maintenance with systems ability, incorporation of innovative O&M strategies etc.) may have and sensors that monitor the wind turbine’s state of operation the potential to narrow this gap in the future. With stronger (e.g. Condition Monitoring Systems) should be underlined. In this winds and fewer conflicting issues than on-land, multi-MW regard, ‘‘ReliaWind’’ project’s (funded under the EU’s 7th Frame- turbines in deeper water depths are likely to dominate the work Programme/duration: 2008–2011) main goal was to offshore sector in the long run in order to maximise energy develop a new generation of more efficient and reliable offshore production, capturing also economies of scale. 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